Retroreflective articles, i.e., articles that return a substantial portion of incident light generally back toward the source, are used widely to make signs that are more visible, e.g., to motorists in approaching vehicles. Perhaps the two most common types of retroreflective materials are microsphere-based products and cube corner type products. Cube corner type products typically can provide brighter retroreflective effect than do microsphere-based materials.
The utility of retroreflective signs is typically limited somewhat to those with an effective light source, e.g., motorists in vehicles. Retroreflective signs are often of less utility to those without an effective light source, e.g., pedestrians, persons in vehicles with malfunctioning headlights, etc. As a result, it is known to provide additional light sources, external illumination such as street lights or internal illumination to improve the visibility of signs having retroreflective portions on the face thereof.
U.S. Pat. No. 4,952,023 (Bradshaw et al.) discloses an internally illuminated sign employing retroreflective sheeting with transmissive bonds. Although very effective, such signs may be unduly bulky for some applications.
Another approach is to use what is sometimes referred to as self-luminous retroreflective articles, e.g., articles that both retroreflect incident light as well as emit light in the same directions.
U.S. Pat. Nos. 5,237,448; 5,243,457; 5,300,783; and 5,315,491 (all Spencer et al.) disclose self-luminescent retroreflective articles. These articles do not provide desired performance.
U.S. Pat. No. 5,415,911 (Zampa et al.) discloses photoluminescent retroreflective sheeting. Such sheetings are not as bright as is desired for some applications.
The need exists for self-luminescent retroreflective sheeting that is brighter and lighter than previously known self-luminescent sheetings.